The interior fan vaulting ceiling, originally installed by Robert and William Vertue, was restored by Sir George Gilbert Scott between 1864 and 1874 The fan vaulting provides structural stability by distributing the weight of the roof down ribs that transfer the force into the supporting columns via the flying buttresses.The cruciform abbey is built of Bath Stone, which gives the exterior its yellow colour. It is an atypical example of the Perpendicular form of Gothic architecture, with low aisles and nave arcades and a tall clerestory. The walls and roofs are supported by buttresses and surmounted by battlements, pinnacles and pierced parapets, many of which were added by George Manners during his 1830's restorations.The nave, which has five bays, is 211 feet (64 m) long and 35 feet (11 m) wide to the pillars and rises to 75 feet (23 m), with the whole church being 225 feet (69 m) long and 80 feet (24 m) wide.